原矿土钻井液室内评价与应用

塔里木盆地大北区块井眼尺寸大，上部地层普遍含砾石，钻井液存在携砂难、沉砂卡钻和压差卡钻风险。目前使用的OCMA膨润土虽然符合OCMA或者API标准，但加入到氯化钾聚合物钻井液中增黏效果有限，配制出的钻井液黏度、切力低，滤失量大，不适合大北区块山前井超大井眼的安全快速钻井。为此，提出了用原矿膨润土替代OCMA膨润土配制钻井液的方法。分析了OCMA膨润土增黏失效的原因，评价了原矿膨润土钻井液的流变性能，滤失造壁性能，配伍性能和抗盐水污染能力。研究了原矿膨润土的粒径分布和比表面积。现场应用表明，原矿膨润土钻井液比OCMA膨润土钻井液具有更好的增黏效果，滤失量更低，井下更安全，能满足大北区块超大井眼的携砂要求，井眼畅通，具有推广应用价值。 

Laboratory Evaluation and Application of A Raw Bentonite Drilling Fluid

Wells drilled in the Dabei block in Tarim Basin have big hole sizes and the top formations have gravels in them, making it difficult for the drilling fluids to carry out drilled cuttings. Pipe sticking by settled cuttings and differential pipe sticking may be encountered because of the big hole sizes and gravels. The OCMA bentonite (conforms to OCMA standard or API standard) presently in use has limited viscosifying effect in KCl polymer drilling fluids; drilling fluids formulated with OCMA bentonite have low viscosity and gel strength, and high filtration rate, and are thus not suitable for use in Dabei block where big holes are drilled in the piedmont structure. To address this problem, raw bentonite is used to replace the OCMA bentonite in formulating drilling fluid. The causes of OCMA bentonite losing its viscosity are analyzed, and the drilling fluids formulated with raw bentonite are evaluated for their rheology, wall building ability, compatibility and saltwater contamination resistance. The particle size distribution and specific surface area of the raw bentonite are studied. Field application shows that drilling fluids formulated with raw bentonite have better viscosifying effect and lower filtration rate than drilling fluids formulated with OCMA bentonite. Use the raw bentonite formulated drilling fluids, downhole conditions are much safer, sand carrying requirement by large hole drilling can be satisfied, and gage hole can be obtained. Field application of the raw bentonite drilling fluids indicates that they are worth spreading.